This invention relates to a process for preparing substituted azetidinones. In particular, it relates to a process for preparing 3.beta.-substituted-amino -4.beta.-halomethyl-1-hydroxyazetidin-2-ones and 3.beta.-alkyl -4.alpha.-halomethyl-1-hydroxyazetidin-2-ones.
Azetidinones substituted in the 4-position by halomethyl are useful intermediates for nuclear analogs of penicillins and cephalosporins, carbapenems, as well as functionalized monocyclic .beta.-lactams. For example, such azetidinones are disclosed by Huffman, W. F., et al., J. Amer. Chem. Soc., 1977, 99, 2352; Salzmann, T. N., et al., J. Amer. Chem. Soc., 1980, 102, 6161; and by Miller, M. J., et al., J. Org. Chem., 1982, 47, 4928. Although synthetic routes to the 4-halomethylazetidinones are known, such routes usually require multi-step elaboration of the 4-halomethyl group after the .beta.-lactam ring has been formed. Because of the importance of substituted azetidinones as intermediates for a variety of .beta.-lactam antibiotics, a more efficient and direct route to these intermediates having the desired stereochemistry would be highly useful.